When an internal combustion engine exhaust valve is open high temperature, high velocity, exhaust gas flows through a well defined passage bounded by the exhaust valve face and its seat. Attendant heat transfer film coefficients are very high and the exhaust valve seat and face are raised in temperature with the exhaust valve face temperature at least double that of a water jacketed exhaust valve seat temperature. When the gas flow is forced to separate from the valve seat, the resulting film coefficient is lowered and the seat operates at a lower temperature. Closure of the exhaust valve with attendant face-seat contact pressure lowers the exhaust valve face temperature.